The present invention relates to a vehicle suspension mounting and to a vehicle suspension incorporating the same, and in particular to a vehicle suspension mounting which provides particularly good performance with regard to dampening and attenuating vibrations.
There are known various kinds of rod type suspensions for vehicles, such as for example the Macpherson strut suspension, in which a telescopic type of Macpherson strut carries a wheel of the vehicle (typically the front wheel) in a rotatable manner at its bottom portion, and is fixed to the vehicle body at its top portion, the bottom portion of said Macpherson strut being rotatable with respect to its top portion about its longitudinal axis, and a compression coil spring being mounted around said Macpherson strut so as to support the vehicle body by pushing the lower portion of the Macpherson strut and the wheel downwards with respect thereto. Now, to maintain the geometry of such a Macpherson strut suspension arrangement, a tie bar or strut is incorporated, which extends from the lower end of the Macpherson strut to which its rearward end is fixed towards the front of the vehicle while angling somewhat upwards and inwards, and which is fixed to the body of the vehicle at its forward end.
When shocks occur to the suspension which impel the wheel backwards with respect to the body of the vehicle, such as when the vehicle goes over a bump in the road or when the vehicle is sharply accelerated or decelerated, then this tie bar is put into severe tension or compression shock, and, although it is required by its rigidity to maintain the vehicle suspension geometry, it ought to be able to yield a little to this tension or compression shock in order to provide good durability and strength. Also, in order to accomodate the upwards and downwards movement of the wheel with respect to the body as the vehicle goes over these bumps or the like, the fixing of the tie bar at its forward end to the vehicle body and/or at its rearward end to the bottom of the Macpherson strut is requried to have a certain flexibility. In view of these considerations, it is known to provide the connection means for mounting the forward end of the tie bar to the body as being a cylindrical cushion rubber member, fixed to the vehicle body by some part of it such as its center, which is held between two retainer members on the tie bar. Thus, this flexible yet firm rubber member provides a cushioning effect against shock which would otherwise be transmitted through the tie bar, and also allows for a certain amount of deformation in the fixing of said tie bar at its forward end to the vehicle body, thus allowing the wheel to move up and down relative to the vehicle body. Also, by internal friction in and plastic deformation of said cusion rubber member of said mounting, it attenuates vibration and shock which are being passed through it from the vehicle wheel and suspension as a whole to the vehicle body. This vibration attenuation can be very important, because alteration of the effective length of the tie bar alters the steering geometry of the vehicle, and in particular alters the amount of toe in of the front wheels. Accordingly, if vibrations are allowed to continue for a long time in the suspension geometry, they can cause troublesome variation of vehicle steering characteristics, and if such vibrations in fact are able to build up they can adversely affect steering quality.
Now, with regard to the construction of this cusion rubber member for the mounting, and with regard to the material therefor, various problems arise. If the elastic coefficient of the rubber is high, then the attenuation of vibration and shock provided thereby is good, but much shock and vibration are transmitted to the vehicle body, and the ride becomes bad. On the other hand, if the elastic coefficient of the rubber is low, then shock and vibration are not severely transmitted to the vehicle body, and the ride becomes good, but the attenuation of vibration and shock is not very good, and build up of steering vibration can occur. Thus, it has been suggested, for example in Japanese Utility Model Publication No. 50-39543 (1975), to provide a suitable shape for the rubber member and the retainer members, so as to provide a low elastic coefficient when the axial load on the tie bar is low, and so as to provide a higher elastic coefficient as said axial load becomes higher, i.e. a so called progressive variation of elastic coefficient of the rubber member with loading on the tie bar.
However, since in the prior art the above described mounting between the forward end of the tie bar and the vehicle body including the cylindrical cushion rubber member is constructed symmetrically and has a symmetrical operational performance, i.e. because the portion of said rubber member which is compressed when the tie bar is put under tension is constructed in substantially the same way as another portion of said rubber member which is compressed when the tie bar is put under compression, thereby the progressive variation of elastic coefficient of the rubber member with loading on the tie bar is substantially the same during compression of the tie bar as during tension thereof, and thus, because over a relatively wide range of movement of the tie bar relative to the vehicle body the elastic coefficient of the rubber member is relatively low, therefore axial vibration of the tie bar may not necessarily be effectively controlled and damped.
In other words, considering for example what happens when the wheel goes over a road bump, as the wheel hits the bump the tie bar is moved in a first direction and one of the portions of the rubber member is compressed, and subsequently when the wheel leaves the bump this portion of the rubber member bounces back and expands and causes the tie bar to be bounced back in the opposite direction, to compress the other portion of the rubber member. Then this other portion of the rubber member rebounds in its turn. This happens repeatedly, and since the coefficient of elasticity of both of the rubber members is fairly low at the initial stage of compression thereof, poor dampening is provided during this reciprocating motion. Thus, axial vibration in the tie bar is not effectively damped, and the toe in of the front wheels can in some circumstances alter in a cyclic manner, thus threatening good steering characteristics. Such problems in the mounting for the tie bar to the body of the vehicle can be very troublesome, and impair good suspension system performance.